Joints and Arthritis

Arthritis is one of the most prevalent chronic health problems worldwide.  In 2002, an estimated 43 million adults in the United States reported being diagnosed by a medical doctor with some form of arthritis, including rheumatoid arthritis, gout, lupus, or fibromyalgia.¹  The impact of arthritis has physical, emotional, social, and fiscal consequences. Approximately 38% (16 million) of adults with doctor-diagnosed arthritis report arthritis-attributable activity limitations, [7.8% of all US adults.]² and 30.6% of adults aged 18-64 with doctor-diagnosed arthritis report an arthritis-attributable work limitation.³  Arthritis and its complications account for a significant portion of the funds allocated to health care dollars.  According to the Center for Disease Control, in 1997, the total cost of arthritis and other rheumatic conditions in the United States was 86 billion dollars.⁴ 

Arthritis is a condition in which the normal articular cartilage is lost.  The damage to the articular cartilage may be related to a variety of factors including genetic predisposition, mechanical overload, metabolic disorders, inflammatory conditions, developmental disorders, and vascular disorders.  Primary osteoarthritis is a non-inflammatory condition without a definite known cause that is characterized by stiffness, pain, joint space narrowing, osteophyte formation, and subchondral cysts.  Secondary arthritis is the destruction of the artricular cartilage related to a known cause (inflammatory, developmental, traumatic, metabolic, etc.)  The pattern, severity, and complications of arthritis can vary depending on the type and location of the arthritis.

There are three types of joints in the human body, each classified by the degree of movement that they allow: immovable, slightly movable, and freely movable.  Immovable joints are synarthroses.  In synarthroses, the bones that comprise the joint are in close contact and separated only by a thin layer of connective tissue.  The lines delineating the bones in the human skull, referred to as suture lines, are examples of synarthroses.  Slightly movable joints are called amphiarthroses.  Amphiarthroses are bones that are connected by fibrous cartilage.  The joint where the ribs meet the sternum is an example of an amphiarthrosis joint.  Finally, the most common type of joint in the adult human body is freely movable — referred to as diarthrosis joints. There are six types of diarthroses joints—ball-and-socket joints, condyloid joints, saddle joints, pivot joints, hinge joints and gliding joints.^{5, 6} 

Ball-and-Socket joints allow the widest range of motion and consist of a spherical end of one bone fitting into a cup shaped socket of another bone. Examples of this type of joint include the shoulder and hip joints.  Condyloid joints are formed by the oval shaped condyle at the end of one bone and the elliptical cavity of another bone.  This type of joint allows for angular motion with limited rotation. Examples of these joints are between the metacarpphalyngeal joints, metatarophalyngeal joints, and the knee.  In saddle joints the surfaces of two bones, each having complementary concave and convex regions, meet—providing a wide range of motion.  The only saddle joint in the human body is in the thumb.  Pivot joints occur where the rounded or conical surfaces of one bone fit into a ring or tendon attached to another bone allowing rotation of one on the other. An example of a pivot joint is the joint between the axis (C1) and atlas (C2) vertebrae in the neck.  Hinge joints are comprised of a convex surface of one bone fitting into a concave depression in another allowing only flexion and extension through a single rotation axis.  The elbow and the interphalyngeal joints are examples of hinge joints.  In gliding joints, flat or nearly flat surfaces move against each other allowing sliding or twisting without circular motion.  The carpal bones in the wrist and the tarsal bones in the ankle are examples of gliding joints.

The Shoulder

The shoulder joint is mainly composed of three bones: the scapula (“shoulder blade”), the humerus (the bone of the upper arm), and the clavicle (“collar bone”).  The glenoid is the articulating portion of the scapula forming the socket of the shoulder.  The shoulder has a relatively shallow socket that allows for a large range-of-motion. The rotator cuff is a group of muscles that function to maintain the humeral head centered in the shallow glenoid as the shoulder is moved.  The four muscles of the rotator cuff are the teres minor, infraspinatus, supraspinatus, and subscapularis.  When the arm is raised, the rotator cuff also holds the humerus tightly in the shoulder socket (glenoid) of the scapula. 

Large muscles around the shoulder (deltoid, biceps, triceps, coracobrachialis, pectoralis, latissimus dorsi) are the motors that, in conjunction with the rotator cuff muscles, move the joint.   In addition to the ribs and spine, the scapula and clavicle are attachment sites for these muscles.  The clavicle attaches to the scapula at a bony process called the acromion.  The acromion is the attachment site for the deltoid and makes up the uppermost part of the shoulder.  There is a bursa (slippery sac of fluid) between the tendons of the rotator cuff and the acromion that allows the tendons to move in the small space with little friction.  There are many bursae throughout the body that function in a similar manner.  These bursa can become inflamed for various reasons, resulting in a condition called bursitis—a separate condition from arthritis (may present in the context of arthritis).

Pain and limited motion around the shoulder is most commonly related to bursitis or tendonitis, and dysfunction of the rotator cuff muscles.  Primary osteoarthritis of the shoulder occurs less frequently than in the hip, knee, and hands.  The most common etiology of secondary osteoarthritis of the shoulder joint is trauma and instability.  Repeated dislocations over many years can cause damage to the cartilage and rotator cuff.  The blood flow to the humeral head can be lost (called osteonecrosis) resulting in collapse of the bone supporting the cartilage and subsequent development of arthritis.  Rheumatoid arthritis can affect the shoulder joint as well but is far less common than osteoarthritis.⁷ 

The Elbow              

As mentioned previously, the elbow is a hinge joint that allows flexion and extension of the arm.  The joint is formed from the humerus (arm), ulna (forearm), and the radius (forearm).  The ulna and radius are the two bones of the forearm and rotate around each other to allow rotation of the hand, thereby allowing one’s palm to face both forward and backward (actions referred to as supinating and pronating).  Stability of the elbow joint is provided by the conforming shape of the ulna and the distal humerus.  The ligaments around the joint and the radius also contribute to the stability.  The triceps, biceps, and brachialis muscles are the primary motors of the elbow joint.

The major causes of elbow arthritis are the inflammatory arthropathies, of which rheumatoid arthritis is the predominant disease process. Approximately 20% to 50% of rheumatoid patients eventually develop arthritis of the elbow.⁹  In addition, involvement of the elbow in juvenile rheumatoid arthritis—a term describing chronic arthritis that begins in childhood—is not an uncommon finding.  The elbow is also the most common site for the formation of rheumatoid nodules beneath the surface of the skin.  Because of their diagnostic and prognostic importance in this disease, it is important to establish their presence.

Other arthritic conditions affecting the elbow include systemic lupus erythematosus (SLE), the seronegative spondyloarthropathies (ankylosing spondylitis, psoriatic arthritis, Reiter's syndrome, and enteropathic arthritis), and crystalline arthritis (gout and pseudogout).  Arthritis of the elbow secondary to repeated trauma can result from fractures within the elbow joint.  When an injury affects the way the elbow joint moves, forces of bone on the articular cartilage surfaces may be increased resulting in inflammation and pain at the joint space.

Though osteoarthritis is the leading cause of arthritis worldwide, osteoarthritis of the elbow is a rare condition, responsible for less than 5% of elbow arthritis.¹⁰  Elbow arthritis usually affects the dominant arm of men in their 50s and, regardless of the etiology, inability to straighten the elbow is a nearly universal complaint.

The Hip and Pelvis

The hip joint is a true ball-and-socket joint.  The socket is the acetabulum and is formed at birth from the presence of a round femoral head articulation with the pelvis.  The acetabulum is formed from three pelvic bones (ilium, pubis, and ischium) that matures and grows until 8 years of age.  Conditions that affect the hip joint at a young age (congenital dislocation of the hip and Perthes’ disease) can result in a socket that is not round.  Thick articular cartilage surrounds the ball and socket portion of the hip and provides a smooth surface that limits friction between the bones with movement. The acetabulum fits tightly around the head of the femur so that, unlike the shoulder, the hip sacrifices some degree of movement for additional stability.

The hip allows movement in three planes of motion including flexion-extension, lateral movement, and rotation. Abduction is movement of the leg away from midline and is limited by the greater trochanter of the femur abutting the outer ridge of the acetabulum. Adduction is movement of the leg towards the midline. Medial rotation is seen by rotating the leg inward about a vertical axis. Lateral rotation is outward about a vertical axis and requires a more extensive anatomical movement of the hip than either adduction, abduction or medial rotation.

Osteoarthritis is the most common cause of hip joint arthritis and, likewise, the most common reason for hip replacement.⁷  Those experiencing osteoarthritis of the hip typically present with pain in the groin, limp, and limited motion.

When viewed from the front, the pelvic bones consist of two hip bones laterally and in front and the ilium and sacrum behind.  The joint between the sacrum and ilium bones (sacroiliac joint) in the pelvis is an example of an amphiarthroses joint.  From birth onward, the iliac cartilage surface is fibrocartilaginous, while the sacral surface is hyaline cartilage. Degenerative arthrosis of the joint begins at an early age in many, affecting the iliac cartilage to a greater extent than its sacral counterpart.¹¹  The early onset of degenerative changes in this location may account for some cases of low back pain in which a cause cannot be definitively established.  Furthermore, in certain rare conditions called spondyloarthropathies, the sacroiliac joint becomes inflamed and arthritic.  Some examples of spondyloarthropathies are ankylosing spondylitis, Reiter's syndrome, the reactive arthropathies, psoriatic arthritis, juvenile spondyloarthropathy, and the axial arthropathy associated with inflammatory bowel disease.

The Wrist and Hand

The wrist is made up of eight small bones called the carpal bones. These bones are interlaced and connect to the radius and ulna in the forearm.  The metacarpal bones are the long bones in the hand that lie mostly underneath the palm, and they are in turn attached to the phalanges—the bones that comprise the fingers and thumbs. The eight bones of the wrist are connected to one another via a vast network of ligaments.  These ligaments provide strength to the bony structure of the wrist while simultaneously providing much-needed mobility.  The carpal bones form two rows with each row functioning together.  The proximal row forms the wrist articulation with the forearm bones (radius and ulna).  The articulation between the proximal and distal carpal rows is called the midcarpal joint. 

Osteoarthritis and rheumatoid arthritis are the two most common causes of wrist arthritis and present with similar symptoms pain and stiffness.  In both types, manifestations include swelling of the wrist, pain, limited motion and weakness.  Extensive swelling of the wrist as a result of active arthritis can compress the nerves that run through the wrist ultimately resulting in carpal tunnel syndrome. Rheumatoid arthritis is also associated with significant deformity related to ligament and tendon disruptions from the associated inflammation.  The so-called “Z-deformity” of the hand and wrist in rheumatoid arthritis may result where the metacarpals angle toward the thumb and the fingers and wrist deviate toward the little finger.⁸

In rheumatoid arthritis, symmetrical fluid collections (effusions) and soft tissue swelling around the metacarpaphalangeal joints and between the first joints of the finger can often be found early on in the disease process.  Late in the disease, the phalangeal joint closest to the nail may be similarly affected.  However, in osteoarthritis the earliest site of involvement is in the phalangeal joint closest to the nail bed and fewer inflamed metacarpophalangeal joints are appreciated.

Functional limitations that occur as a result of arthritis of the wrist include inability to perform heavy lifting and gripping secondary to pain, as well as inability to perform fine motor functions because of limitations in one’s range of motion.  Activities of daily living such as shaving or applying shampoo may be limited as well.

The Knee

The knee, which is the largest joint in the body, is comprised from three bones—the tibia and fibula in the lower leg and the femur in the upper leg.  The surfaces where each of these bones come together are covered with hyaline cartilage.  The primary articulation of the knee and, therefore, the point of maximum weight bearing, is between the femur and tibia.  This articulation is separated into the medial and lateral compartments separated by the cruciate ligaments in the center of the knee.  The tibial surface (tibial plateau) is convex in the lateral compartment and concave in the medial compartement.  Both tibial surfaces are relatively flat compared with the round femoral condyles of the distal femur.  Fibrocartilage structures, called menisci, fill the spaces created by the different shapes of the bones and assist in the even distribution of stress through the knee.  The collateral ligaments stabilize the knee in the coronal plane (i.e. sideways).  The anterior and posterior cruciate ligament (located in the center of the knee) act together to provide resistance to rotational and sagittal plane (i.e. front to back) stability.  The patellar ligament forms a synovial with the knee cap or patella. The patella is a sesamoid bone that is contained within the tendon of the quadriceps muscle and forms a gliding type joint with the distal femur.  The gliding of the underside of the patella within the groove of the femur allows for increased efficiency of the quadriceps muscle when contracting.

Many arthritic conditions can result in degeneration of the joint space in the knee.  The most common cause of the arthritic knee and, likewise, the most frequent reason for knee replacement is primary osteoarthritis.  Any damage to the ligaments, meniscus, or bones near the knee joint, including fractures of the knee, can lead to degeneration of the joint many years after the injury was originally sustained.  Classic clinical criteria that must be met for the diagnosis of osteoarthritis of the knee include the presence of knee pain plus at least three of the following six characteristics¹²: greater than 50 years of age, morning stiffness of less than 30 minutes, crepitus, bony tenderness, bony enlargement, and no palpable warmth.

The knee manifests many changes during the course of rheumatoid arthritis.  Thickening of the tissue surrounding the patella and fluid within the joint space are two common findings.  In addition, the ligaments of the knee may become increasingly more flaccid, eventually resulting in deformities of the knee and atrophy of the quadriceps muscle.⁷  The area behind the knee that contains the popliteal artery, termed the popliteal fossa, may harbor what’s known as a Baker’s cyst in those with a history of arthritis.  Baker’s cyst is commonly the result of a meniscus tear.

Interestingly, the knee is involved in more than 50% of the cases of established bacterial arthritis.⁷  This arthritic infection may result from a bite or trauma, from direct inoculation of bacteria during a surgical procedure or, rarely, secondary to infection of an adjacent bone.

The Ankle and Foot

In testament to the complex interplay of the bones and joints of the foot and ankle, together the ankle and foot are comprised of an astonishing 26 bones and 33 joints.  During the simple motion of walking, there is a complex interplay ongoing at each of these joints.  The ankle joint itself primarily consists of the articulation of three bones: the lower end of the tibia, the fibula and the talus bone in the foot.  The tibia and fibula fit into grooves on the surface of the talus.  It is the interaction between the tibia and talus at this groove that allows rotation of the ankle.  The fibula functions primarily to prevent lateral displacement and over-rotation of the tibia on the talus. 

The talus sits on top of the calcaneus bone (heel of the foot) forming the subtalar joint. The ankle joint mainly allow your foot to move either up (dorsiflexion) or down (plantarflexion).  The subtalar joint allows rotation of the foot and plays an important role for stabilizing the arch during weight bearing and allowing for flexibility at other times.

The bones of the foot are similar in organization to the bones of the hand. The foot is subdivided into three main parts: the forefoot, the midfoot, and the heel. The forefoot is composed of the five toes (called phalanges) and the long bones (metatarsals) that connect the toes to the midfoot.  Each toe (phalanx) is made up of several small bones. The big toe (hallux) has two phalanges, two joints (interphalangeal joints), and two small, round sesamoid bones that function to assist in moving the big toe up and down.  Each of the other four toes has three bones and two joints. The phalanges are connected to the metatarsals by five metatarsal-phalangeal joints at the ball of the foot.  The midfoot has five tarsal bones and forms the arch of the foot. The bones of the midfoot are connected to the forefoot and the hindfoot by several strong ligaments, muscles, and the plantar fascia that lines the sole of the foot.  The hindfoot consists of three joints and acts as the bridge between the midfoot and the talus.

The ankle is commonly affected by inflammatory conditions such as rheumatoid arthritis.  Primary osteoarthritis of the ankle is rare; however, the foot and ankle are commonly in injured with traumatic events leading to post-traumatic arthritis.  Arthritis of the ankle can lead to diffuse swelling around the joint between the talus and the tibial.  If extensive, the swelling may actually impinge upon the posterior tibial nerve and result in decreased sensation in the feet.⁷

Similar criteria that were used to establish the diagnosis of osteoarthritis in the hand have been employed to establish its presence in the foot.  In the case of rheumatoid arthritis, tenderness of the metatarsal-phalangeal joints may be marked, resulting in the tendency to walk on one’s heels and to hyperextend the toes.  Furthermore, erosive damage to the joint spaces within the foot can result in a drifting of the toes toward the small toe and movement of the metatarsal heads upward resulting in what’s referred to as a “cock-up” deformity.⁷

Gouty arthritis characteristically initially presents in the lower extremity in one joint (monoarticular)—in particular, often affecting the base of the great toe (first metatarsophalangeal joint).  Acute gout is intensely inflammatory with swelling, redness, and disabling pain often apparent.

In summary, the human body has many joints of various shapes and sizes.  The complex interaction taking place at these joints enables for the defining characteristic of life on earth—motion.  Consequently, we are dependent upon proper functioning of these joints to live fully, healthy and complete lives.  It is this fundamental truth of life that underscores the damage to society that can result in the wake of arthritis.  By understanding more fully the joints to which arthritis may lay waste, one can better appreciate the disease process and, hopefully, make strides toward its management.

Authors:  Ryan P. Dunlay, B.A., University of Iowa Medical School, Iowa City, IA

                Michael O’Rourke, M.D., University of Iowa Hospital, Iowa City, IA

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